Currently, to the best of Applicants' knowledge, “snap top” dispensing lids are made from polypropylene due to its toughness. While polyethylene has been disclosed as being suitable it is not used in these applications. However, it is desirable from a recycling point of view to use polyethylene rather than polypropylene.
U.S. Pat. No. 4,047,495, issued Sep. 13, 1977 to O'Brian, assigned to Polytop Corporation teaches a “snap top” child proof lid for a container. The patent teaches the living hinge is preferably injection molded from polypropylene because of the well-known living hinge properties of polypropylene. Other olefin polymers can be used but are not preferred (Col. 4, lines 41-50). The patent teaches away from other polyolefins, such as polyethylene.
U.S. Pat. No. 4,638,916, issued Jan. 27, 1987 to Beck et al., assigned to Owens-Illinois, Inc., teaches a snap type hinge cap. The structural elements of the lid are disclosed but there is no disclosure of what material the lid may be made from. One of ordinary skill in the art would likely select polypropylene as the preferred material.
U.S. Pat. No. 5,148,912, issued Sep. 22, 1992 to Nozawa, assigned to Yoshino Kogyosho Co., Ltd., teaches a slightly different snap top lid in which there are two separate hinges or straps. Again the structural elements are clearly defined but the composition of the cap is not clearly specified. One of ordinary skill in the art would likely select polypropylene as the preferred material.
U.S. Pat. No. 6,041,477, issued Mar. 28, 2000 to Rentsch et al., also teaches the structural elements of a snap top lid which differ from the prior art. While the patent contains a warning about residual stress in snap top lids having adverse effects on injection moulding plastic material, (Col. 3, lines 28 to 35), nowhere in the specification is there a disclosure of suitable materials from which to make the hinge.
U.S. Pat. No. 6,766,926, issued Jul. 27, 2004 to Elchert, assigned to Owens-Illinois Closure Inc., teaches the type of closure most commonly seen today. The structural elements of the cap are clearly disclosed. However, again the material form which the cap may be made is not discussed.
A need exists to provide a polyethylene composition suitable for use in injection molding having a high resistance to cracking on repeated flexing.